"The drug," the Doctor said, turning his head and coughing to clear out the last of the congestion. "Must've been the final leg for it. If nothing else killed you, the lack of oxygen would. It's really clever, the efficiency with which they kill."

He took in a few more breaths and leaned back, relaxing in Jack's embrace. They would make it out of this together. In this cave, it only became more obvious to the Doctor that while they were more often than not the reason for their own troubles, they managed to get out of them, too.

They were, as Jack had said, good for each other.

"Thank you," he said, nodding.